The present invention relates to couplings such as are employed in creating a movable junction between separate lengths of electrical metallic tubing in a run thereof so as to permit the expansion and contraction of such electrical metallic tubing in response to changes in temperature, etc. More particularly, the present invention relates to such an expansion coupling adapted to facilitate the simple and efficient interrelation thereof with the separate lengths of electrical metallic tubing.
It is conventional in many applications to run electric wiring within a relatively thin-walled metal tubing. In large scale installations involving extended runs of such tubing it is commonplace to position what are known as expansion couplings between separate lengths of tubing in order to allow for longitudinal expansion or contraction of the tubing as necessary in response to longitudinal expansion or contraction of the tubing material, such as may be occasioned by variations in temperature (as determined by the tubing material""s coefficient of expansion), or by the expansion or contraction of the structure in which the run of tubing is installed, such as, for instance, at structural expansion joints. For runs of tubing for electrical wiring in particular, the National Electrical Code requires the employment of such expansion couplings at all building expansion joints.
Electrical metallic tubing (xe2x80x9cEMTxe2x80x9d), also known and referred to as thin-wall tubing because it is thinner than rigid metal tubing, is routinely employed as conduit for electrical wiring.
Broadly speaking, expansion couplings function to interconnect the terminal ends of separate lengths of tubing in a single run and permit sliding movement of one length of tubing relative to the other, as necessary, to accommodate expansion and contraction.
A conventional expansion coupling 5 for joining electrical wiring tubing, depicted in FIG. 1, includes a metal reducer 6 having one end threaded onto an end of a first length of tubing 7, and another end threadingly connected to a cylindrical metal sleeve 8. Threadingly connected to an opposite end of the sleeve 8 is a metal gland nut 9 encompassing a fiber gasket 10, a steel washer 11, and a packing 12 of asbestos and copper braid. The second length of tubing 13 passes through the packing 12, which is compressed against the tubing by tightening the gland nut 9. A plastic throat bushing 14 is threadingly connected to the end of the second length of tubing 13 to provide a smooth inner diameter against which the wires can engage.
Conventional expansion couplings, including such as described above, are routinely made from rigid metal, making them bulky. Such couplings are cumbersome to employ and, owing to their multitude of components, expensive to manufacture. In joining separate lengths of EMT, such conventional, rigid-metal expansion couplings must be retro-fitted in order to work properly with the thin-walled EMT. And particularly for indoor applications, where rain, snow, and the like are not a consideration, conventional expansion couplings such as the one described above are unnecessarily complicated in construction and operation.
Philibert, U.S. Pat. No. 3,885,821, discloses an expansion fitting adapted for coupling EMT, the fitting itself comprising a sleeve of EMT. While advantageous over prior art rigid metal expansion couplings, the Philibert device nevertheless suffers from several drawbacks, most notably in operation. More particularly, the Philibert device must be coupled to lengths of EMT by crimping or rolling the sleeve of the fitting after the ends of the lengths of EMT are inserted therein. In consequence, employment of the Philibert device in the fieldxe2x80x94that is, under actual installation conditionsxe2x80x94is rendered problematic by the need to crimp the sleeve following insertion of the lengths of EMT to be joined.
It would therefore be desirable to provide an expansion coupling for EMT that is at once economical to manufacture and well suited for the simple and efficient joining of separate lengths of tubing in a given application, and which addresses the other limitations of prior art expansion couplings.
The specification describes an expansion coupling for connecting separate first and second lengths of electrical metallic tubing to permit relative axial movement between the first and second lengths of electrical metallic tubing. According to the disclosure, the expansion coupling more particularly comprises a sleeve of thin-walled metal tubing having a principal length and an interior axial passageway terminating in opposing first and second openings. The first opening is dimensioned to receive therein a terminal portion of the first length of electrical metallic tubing in telescopic sliding relationship. A movable member is positioned proximate the second opening, the movable member being selectively positionable within the axial passageway to secure the second length of tubing in a fixed relationship with the sleeve. A stop extending into the passageway defines an inward limit of telescopic sliding movement for the first length of electrical metallic tubing relative to the coupling.
According to one feature of this invention, the movable member comprises a set screw that is selectively positionable within the passageway to secure the second length of electrical metallic tubing in fixed relationship with the coupling.
According to another feature of this invention, the wall of the sleeve is circumferentially indented to thereby define the stop.